數組去重(JavaScript中數組去重的示例分析)

一、前言:

我們在實際工作中,或者在面試找工作時,都會用到或者被問到一個問題,那就是“數組如何去重”。是的,這個問題有很多種解決方案,看看下面的十種方式吧!

二、數組去重方式大匯總:

Methods 1: 思路:定義一個新數組,并存放原數組的第一個元素,然后將元素組一一和新數組的元素對比,若不同則存放在新數組中。

functionunique(arr){varres=[arr[0]];for(vari=1;i<arr.length;i++){varrepeat=false;for(varj=0;j<res.length;j++){if(arr[i]===res[j]){repeat=true;break;}}if(!repeat){res.push(arr[i]);}}returnres;}console.log('------------方法一---------------');console.log(unique([1,1,2,3,5,3,1,5,6,7,4]));

Methods 2: 思路:先將原數組排序,在與相鄰的進行比較,如果不同則存入新數組。

functionunique2(arr){vararr2=arr.sort();varres=[arr2[0]];for(vari=1;i<arr2.length;i++){if(arr2[i]!==res[res.length-1]){res.push(arr2[i]);}}returnres;}console.log('------------方法二---------------');console.log(unique2([1,1,2,3,5,3,1,5,6,7,4]));

Methods 3: 利用對象屬性存在的特性,如果沒有該屬性則存入新數組。

functionunique3(arr){varres=[];varobj={};for(vari=0;i<arr.length;i++){if(!obj[arr[i]]){obj[arr[i]]=1;res.push(arr[i]);}}returnres;}console.log('------------方法三---------------');console.log(unique3([1,1,2,3,5,3,1,5,6,7,4]));

Methods 4: 利用數組的indexOf下標屬性來查詢。

functionunique4(arr){varres=[];for(vari=0;i<arr.length;i++){if(res.indexOf(arr[i])==-1){res.push(arr[i]);}}returnres;}console.log('------------方法四---------------');console.log(unique4([1,1,2,3,5,3,1,5,6,7,4]));

Methods 5: 利用數組原型對象上的includes方法。

functionunique5(arr){varres=[];for(vari=0;i<arr.length;i++){if(!res.includes(arr[i])){//如果res新數組包含當前循環itemres.push(arr[i]);}}returnres;}console.log('------------方法五---------------');console.log(unique5([1,1,2,3,5,3,1,5,6,7,4]));

Methods 6: 利用數組原型對象上的 filter 和 includes方法。

functionunique6(arr){varres=[];res=arr.filter(function(item){returnres.includes(item)?'':res.push(item);});returnres;}console.log('------------方法六---------------');console.log(unique6([1,1,2,3,5,3,1,5,6,7,4]));

Methods 7: 利用數組原型對象上的 forEach 和 includes方法。

functionunique7(arr){varres=[];arr.forEach(function(item){res.includes(item)?'':res.push(item);});returnres;}console.log('------------方法七---------------');console.log(unique7([1,1,2,3,5,3,1,5,6,7,4]));

Methods 8: 利用數組原型對象上的 splice 方法。

functionunique8(arr){vari,j,len=arr.length;for(i=0;i<len;i++){for(j=i+1;j<len;j++){if(arr[i]==arr[j]){arr.splice(j,1);len--;j--;}}}returnarr;}console.log('------------方法八---------------');console.log(unique8([1,1,2,3,5,3,1,5,6,7,4]));

Methods 9: 利用數組原型對象上的 lastIndexOf 方法。

functionunique9(arr){varres=[];for(vari=0;i<arr.length;i++){res.lastIndexOf(arr[i])!==-1?'':res.push(arr[i]);}returnres;}console.log('------------方法九---------------');console.log(unique9([1,1,2,3,5,3,1,5,6,7,4]));

Methods 10: 利用 ES6的set 方法。

functionunique10(arr){//Set數據結構,它類似于數組,其成員的值都是唯一的returnArray.from(newSet(arr));//利用Array.from將Set結構轉換成數組}console.log('------------方法十---------------');console.log(unique10([1,1,2,3,5,3,1,5,6,7,4]));

三、其他:

有意思的是,當我把數組的長度變得很大的時候(如下所示),測試了一下不同方法的執行時間長短,會發現方法三、四、五、六、七相對來說會更有優勢,而方法八的執行速度似乎一直墊底。你也可以在你本地跑一下試試!

//測試用的超大數組
var arr = 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//這里只是舉例方法三(如果你把所有方法放在一起測試,會更直觀的看到執行時間的差異)

vartime3=newDate().getTime();functionunique3(arr){varres=[];varobj={};for(vari=0;i<arr.length;i++){if(!obj[arr[i]]){obj[arr[i]]=1;res.push(arr[i]);}}returnres;}console.log('------------方法三---------------');console.log(unique3(arr));console.log('3所花時間:'+(newDate().getTime()-time3));